package org.apache.lucene.search.spans;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import org.apache.lucene.search.Weight;
import org.apache.lucene.search.Scorer;
import org.apache.lucene.search.Explanation;
import org.apache.lucene.search.Similarity;

class SpanScorer extends Scorer {
    private Spans spans;
    private Weight weight;
    private byte[] norms;
    private float value;

    private boolean firstTime = true;
    private boolean more = true;

    private int doc;
    private float freq;

    SpanScorer(Spans spans, Weight weight, Similarity similarity, byte[] norms) throws IOException {
        super(similarity);
        this.spans = spans;
        this.norms = norms;
        this.weight = weight;
        this.value = weight.getValue();
    }

    public boolean next() throws IOException {
        if (firstTime) {
            more = spans.next();
            firstTime = false;
        }

        if (!more)
            return false;

        freq = 0.0f;
        doc = spans.doc();

        while (more && doc == spans.doc()) {
            int matchLength = spans.end() - spans.start();
            freq += getSimilarity().sloppyFreq(matchLength);
            more = spans.next();
        }

        return more || freq != 0.0f;
    }

    public int doc() {
        return doc;
    }

    public float score() throws IOException {
        float raw = getSimilarity().tf(freq) * value; // raw score
        return raw * Similarity.decodeNorm(norms[doc]); // normalize
    }

    public boolean skipTo(int target) throws IOException {
        more = spans.skipTo(target);

        if (!more)
            return false;

        freq = 0.0f;
        doc = spans.doc();

        while (more && spans.doc() == target) {
            freq += getSimilarity().sloppyFreq(spans.end() - spans.start());
            more = spans.next();
        }

        return more || freq != 0.0f;
    }

    public Explanation explain(final int doc) throws IOException {
        Explanation tfExplanation = new Explanation();

        skipTo(doc);

        float phraseFreq = (doc() == doc) ? freq : 0.0f;
        tfExplanation.setValue(getSimilarity().tf(phraseFreq));
        tfExplanation.setDescription("tf(phraseFreq=" + phraseFreq + ")");

        return tfExplanation;
    }

}
